The art is replete with teachings describing various semipermeable membranes, their preparation and use. U.S. Pat. No. 3,350,844 teaches the enrichment of gases by permeation through a thin permeable film or membrane prepared from a polyarylene oxide film. U.S. Pat. No. 3,780,496 teaches the use of sulfonated polyxylene oxide membranes to separate helium, hydrogen and oxygen from gas mixtures.
While the membranes of the above teachings and others all display some level of utility, there exists a continuing search for new membranes and new applications for both new and known membranes. One application where the use of membrane technology may prove beneficial is in the separation of gaseous carbon dioxide-methane mixtures into enriched fractions of their constituent parts. Natural gas is generally found in combination with carbon dioxide. Removal of the carbon dioxide from the natural gas is desirable because it results in both a product (purified natural gas) of greater commercial worth and it provides purified carbon dioxide useful for other applications, such as enhanced oil recovery. Conventional separation processes generally employ cryogenic methods which are relatively energy intensive.